How can the company that did so well on the update mechanism of Chrome do so badly on the update mechanism of Android?

On Chrome almost everyone around the world will always use the newest version just a few days after it is available without any breakage so far.

On Android every manufacturer (and their customer) is left to its own update-mechanism severely hindering advancements and making an enormously big parts of the phones "rooted and custom modded".

And even the techforums can't seem to agree about what way Android is going in the next versions. Will the "2" branch be for phones only and the "3" branch for tablets only? Will 2.4 be just a minor update? When will 2.4 and 3.0 be out and what about 3.1 and who will get it and who won't?

Android should be much more like a basic layer (OS) that other manufacters can put customisations on top (apps, shells, themes). But it seems to go the way of '1000 Linux distributions that all need to do their own testing and adopting of new versions'